The cysteinyl leukotrienes are products of the 5 lipoxgenase pathway of arachidonic acid metabolism and are synthesized by mast cells, basophils, macrophages, and eosinophils. The objectives are 1) to determine the effectiveness of 3 different doses of pranlukast and placebo at inhibiting leukotriene-D4 induced bronchoconstriction, 2) to characterize the relationship B/N plasma concentrations of pranlukast and inhibition of LTD4-induced bronchocons. And 3) to evaluate the safety of the various intravenous doses of pran. during inhalation.